The present invention is directed to electron beam or EB curing of emulsion-based pressure-sensitive adhesives to provide a pressure-sensitive adhesive with superior elevated temperature shear properties.
Concern over the environment has made attractive pressure-sensitive adhesive polymers formed by emulsion polymerization, as opposed to polymerization in organic solvents. Emulsion polymers can be coated onto a substrate, e.g. face material, release liner, and/or a transfer surface, and a pressure-sensitive adhesive layer formed upon water evaporation.
The possibility of preparing a pressure-sensitive adhesive in an emulsion and UV curing of pressure-sensitive adhesives has been mentioned in the art. Examples include U.S. Pat. No. 3,637,615 to Coffman, U.S. Pat. No. 4,069,123 to Skoultchi et al and U.S. Pat. No. 4,185,050 to Lazear et al. This art has however only illustrated the preparation of polymers in an organic solvent and not in an aqueous media and therefore the effect of UV curing on a polymer prepared in an aqueous media has not been demonstrated.
We have found emulsion-based pressure-sensitive adhesives to have poor high-temperature peel and shear properties.
It is the purpose of the instant invention to provide a technique to improve the high-temperature performance of emulsion-based pressure-sensitive polymers without sacrificing significantly the ambient temperature performance.